Hi Vishnu

The username argument is supposed not to be passed as null in this case.
Is it possible that the Engine is already streaming when "setUserName" is called?
Are you using "createEngine" or the old "loadEngine" in order to load the Engine?
May you please check Lightstreamer Server log? You should be able to find your username logged.

I Assume that, in your second question, you are looking for an alternative to using "NonVisualTable" still in the context of an HTML front-end. Then the answer is no; subscribing to items is only made through the definition of a table object.
Other types of table objects do exist, as listed in the Javascript API JSDocs: they all are "visual tables" and can be used in order to take advantage of Lightstreamer-provided management of the visualization of the data in the table cells.

Dario